(a) Field of the Invention
This invention relates to mono-, bis- and tris-(1 and/or 2 substituted-3-indolyl)-substituted-2-furanones useful as color precursors, particularly in the art of carbonless duplicating as, for example, in pressure-sensitive systems and in thermal marking systems; to substituted butanoic and butenoic acids useful as intermediates to these furanones; and to processes for preparing said indolyl-substituted furanones, butanoic acids and butenoic acids.
(b) Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as colorless precursors to dyestuffs. Said precursors have applications in the art of dyeing and coloring, for example, in the dyeing and printing of textiles and in the art of carbonless duplicating. Among the more important classes useful in the carbonless duplicating art, there may be named phenothiazines, for example, benzoyl leuco methylene blue; phthalides, for example, crystal violet lactone; fluorans, for example, 2'-anilino-6'-diethylaminofluoran and 2'-dibenzylamino-6'-diethylaminofluoran; and various other types of colorless precursors currently employed in commercially accepted carbonless copy systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 2,712,507, 2,800,457 and 3,041,289. However, to the present time, there appears to be no evidence that the indolyl-substituted furanones constituting the subject matter of this invention have been employed as color formers, particularly in carbonless duplicating systems or in thermal marking systems. Representative of thermal marking sysems disclosed in the prior art are those described in U.S. Pat. Nos. 3,539,375 and 3,895,173.
Rees and Sabet in the Journal of the Chemical Society, 687-691 (1965), Chemical Abstracts 62: 6475h (1965), describe the preparation and physical characteristics of 3,4-dichloro-5-(3-indolyl)-2(5H)-furanone and 3,4-dichloro-5-(2-methyl-3-indolyl)-2(5H)-furanone without giving any indication of their utility. Barrett, Beer, Dodd and Robertson in the Journal of the Chemical Society, 4810-4813 (1957) Chemical Abstracts 52: 10053e (1958) describe the preparation and the physical characteristics of 5-(1-acetyl-5-substituted-3-indolyl)-2(3H)-furanones. The compounds are described as intermediates in a structural confirmation synthesis. We have now discovered that the compounds described by Rees and Sabet are readily converted to colored substances on thermal exposure. This property makes them useful for incorporation into thermal marking systems such as are used in recording and in duplicating systems.
Diels and Alder in Annalen Der Chemie 490: 277-294 (1931), Chemical Abstracts 26: 438 (1932), describe the preparation and physical characteristics of 2,4-bis(2-methyl-3-indolyl)-4-oxobutanoic acid and 2,4-bis(1,2-dimethyl-3-indolyl)-4-oxobutanoic acid. There is no indication of the utility of the compounds given in the reference. Jackson and Naidoo in Journal Chemical Society, Perkins Transactions II; (5): 548-551 (1973), Chemical Abstracts 78: 12439h (1973), describe the preparation and physical characteristics of 4-(2-methyl-3-indolyl)-4-oxobutanoic acid as a chemical intermediate for the preparation of the corresponding methyl ester for which no utility is given.